This invention relates to pipes heated using electrical heaters, and more particularly to such pipes using a distributed flat heater made of tape or braided wire, preferably using a tape made of an amorphous alloy.
Heretofore, various devices and methods have been devised to produce pipes including electrical heater means to heat a liquid therein. The relatively high cost prevented widespread use of these pipes.
A measure of flexibility is required of heated pipes to allow installation in various locations under constraints of size and shape of available space. Heated pipes known in the art are mainly rigid and do not easily adapt to these constraints.
Other pipes known in the art do not have any provisions to heat the liquid therein, but require heat to be applied externally, if possible.
For example, Zelinka et al., U.S. Pat. No. 4,484,061, details a temperature control system for a liquid chromatographic column including a thin film heater/sensor comprising a foil-like patterned heating element adhesively mounted between a pair of flexible electrically insulative layers.
Blomquist G., U.S. Pat. No. 5,431,762, details a method of joining the ends of spirally wound thermoplastic pipes; it comprises working the ends with stepped faces. A stainless steel band is then applied over the gap, and heated to 100 deg.C. An internal extruder is then rotated around the inside of the gap to form a thermoplastic weld which is allowed to cool before the band is removed.
Dommer A. and Dommer D., U.S. Pat. No. 5,225,030, detail an arrangement for (internally) welding the (longitudinal) joints between sections assembled to form a hollow plastic profile in which a device of heating bars and pressure pads is drawn through the assembly to weld plastic filler strips into the joints. Preferably the traction device carries opposed heating bars containing cartridge heaters and thermosensors, which plastify the joint edges of the profiles and plastics welding strips with tear-resistant cores, e.g. steel wires.
Sopory U., U.S. Pat. No. 5,432,323, details a strip heater which has one elongate control element, one elongate heating element and a number of elongate conductors. An electrical insulator partially encloses the elements and the conductors. The elements are physically separated and electrically connected by one of the conductors such that both of the elements can be simultaneously placed in relative thermal contact with an object to be heated.
Alternatively a dividing strip separates the heating element from the control element and at a fixed distance so that the heating element is maintained generally parallel to the control element.
Yurkin V., RU Patent 2036063, details a method consisting of cutting a metal strip into blanks, winding the blanks in several turns around a forming drum, welding the inner and outer seams, and butt welding the resultant shells to produce a pipe. The method is characterised by the following features: (a) the metal strip is produced by hot rolling; (b) cutting into blanks takes place immediately after the rolling process; (c) an easily melting metal in powder or strip form, with a melting point below 1100 deg.C., is applied to the drum in the winding process while the blank temp. is not below the melting point of this metal.
AMT Ltd. patent application Ser. No. 08/292685 details the use of amorphous metallic ribbon for electrical heating, and the use of the Manov process. In an article by Manov et al. entitled "The Influence Of Quenching Temperature On The Structure And Properties Of Amorphous Alloys," published in Materials Science and Engineering, A133 (1991) 535-540, an "overheating" technique is disclosed. By overheating the melt and then lowering the temperature before actually forming an amorphous metallic ribbon from it, it is possible to produce a ribbon with improved characteristics, such as higher and more stable resistivity. As used herein, the term overheated metallic alloy ribbon refers to a metallic alloy ribbon made from a melt which has been overheated as described by Manov et al. Although the reproducibility of results is not mentioned, that is in fact another advantage of overheating. (The Manov et al. article provides good general background reading on amorphous ribbons.
Olovyanishnikov V. et al., SU Patent 1819223, details a reinforced thermoplastic-pipes production method--has lengthwise steel-wire reinforcing elements applied with heating, followed by steel-tape wound helically in opposite directions and protective cover, with final heating.
Used in manufacturing of hose-like articles, e.g. flexible reinforced tubes for conveying aggressive liquids and gases in petroleum, petroleum-processing, chemical, etc. industries.
DABINETT J. and MILLWARD W., Patents WO 9413992, AU 9455729, EP 625251 and EP 625252, detail a method of producing composite pipe for use in oil, gas, water and chemical industries--has core of helically wound steel strip embedded in plastics matrix, with outer lining of glass fibre filament.
The pipe is produced on a heated rotating mandrel coated with a release agent. The inner surface may be polyester veil impregnated with epoxy resin. G.R.P. lining is wound from glass fibre filaments previously passed through a resin bath.
A steel strip is wound onto the uncured wet resin and an epoxy resin simultaneously applied. The outer lining is of glass fibre filament previously passed through a resin bath. Heat is applied whilst rotating to cure the resin. The mandrel is removed after cooling. ADVANTAGE--Improved strength, stiffness and corrosion and abrasion resistance.
Hynes U.S. Pat. No. 3,286,078 details a flexible internal heater. A flexible metal tubing contains insulated flexible resistors. The metal tubing is mounted inside a flexible hose conduit to heat liquid therein.
Manov et al., U.S. Pat. No. 5,641,421, details an amorphous metallic alloy electrical heater system.
HITACHI METALS LTD, JP 5340494, details plastic pipe coupling--using electric wire, wherein electric wire is embedded in the inner surface of a coupling body. By generating heat of the electric wire, the outer surface of a resin pipe inserted in the connection end part of the coupling body is heated and coupling body and the resin pipe are fused and connected together.
Disadvantages of these devices and methods include the relatively high cost, difficulty in flexing the pipes to adapt to installation constraints and lack of electrical heating capability in part of the abovementioned devices.
Moreover, pipes joined according to JP 5340494 have a nonuniform, rugged shape because of the uncontrolled heating process.